a) Field of the Invention
The present invention relates to a field emission element with antireflection film and a method of manufacturing a field emission element, and more particularly to a field emission element with a having a field emission cathode tip from which electrons are emitted, and a method of manufacturing a field emission element.
b) Description of the Related Art
A field emission element emits electrons from a sharp tip of an emitter (field emission cathode) by utilizing electric field concentration. For example, a flat panel display can be structured by using a field emitter array (FEA) having a number of emitters disposed in array. Each emitter controls the luminance of a corresponding pixel of the display.
FIGS. 16A to 16F illustrate a conventional manufacture method of a field emission element.
As shown in FIG. 16A, a conductive gate electrode film 62 is formed on a substrate 61, and a resist pattern 63 having a predetermined shape is formed on the gate electrode film 62 through photolithography.
Next, by using the resist pattern 63 as a mask, the gate electrode film 62 is anisotropically etched to leave a gate electrode 62a with a gate hole 67 having a circular plan shape (as viewed from the upper shape), as shown in FIG. 16B. This etching reduces the thickness of the resist pattern 63 so that a thin resist pattern 63a is left.
Next, as shown in FIG. 16C, after the resist pattern 63a is removed, a sacrificial film 64 is isotropically deposited on the surface of the gate electrode 62a and on the exposed surface of the substrate 61.
Next, as shown in FIG. 16D, the sacrificial film 64 is anisotropically etched to leave a sacrificial film (side spacer) 64a on the inner wall of the hole 67 of the gate electrode 62a, the sacrificial film 64a reducing its opening diameter toward the substrate.
Next, as shown in FIG. 16E, an insulating film 65 is deposited on the whole substrate surface, and a conductive emitter electrode 66 is formed on the insulating film 65.
Next, as shown in FIG. 16F, the whole of the substrate 61 and side spacer 64a and part of the insulating film 65 are etched and removed, leaving a peripheral insulating film 65a between the gate electrode 62a and emitter electrode 66.
As a positive potential is applied to the gate electrode 62a, an electric field can be concentrated upon the tip of the emitter electrode (cathode) 66 so that electrons are emitted from the emitter electrode 66 toward an anode electrode (not shown).
The gate electrode 62a surrounds the gate hole 67 and is made of two parts (laterally separated regions) as viewed in section. A distance between these two parts in the horizontal direction is called a gate diameter. A voltage to be applied to the gate electrode 62a is determined by the gate diameter.
The resist pattern 63 having a predetermined shape shown in FIG. 16A is formed through photolithography. First, a resist film (photosensitive resin) is formed on the whole surface of the gate electrode film 62, and thereafter exposed and developed to form the resist pattern 63 having a predetermined shape.
It is not preferable if during the exposure, an amount of light reflected from the gate electrode film 62 under the resist film 63 is large. The gate electrode film 62 is made of metal or semiconductor having a low resistivity. However, metal and semiconductor has generally a large reflectance.
During the exposure, light passes through the resist film 63 and is reflected by the gate electrode film 62 so that an area not desired is also exposed. This reflected light becomes more influential particularly when the surface of the gate electrode film 62 has steps. In such a case, the resist pattern 63 after the development cannot have a desired shape. Therefore, if this resist pattern 63 is used as a mask and the etching process illustrated in FIG. 16B is performed, the gate electrode 62a having a desired pattern cannot be formed.
If the resist film 63 is a positive resist film, the gate electrode 62a is likely to have a compression or a disconnection, whereas if the resist film 63 is a negative resist film, the gate electrode 62a is likely to have a projection or a bridge.
The following problems also occur.
(1) Multiple interferences during exposure change with a thickness of the resist film 63 so that the sizes of gate electrodes have a variation. PA1 (2) If there is a reflectance variation in gate electrode films 62, the sizes of gate electrodes have a variation. PA1 (3) Since a standing wave is generated in the resist film 63, a resolution of the resist film 63 lowers. PA1 (4) It is necessary to use a thick resist film 63 because an etching selection ratio of the resist film 63a to the gate electrode film 62a during the etching process (FIG. 16B) is low. For example, if the gate electrode film 62 has a thickness of 0.3 .mu.m, it is necessary to use the resist film 63 having a thickness of 0.8 .mu.m or more. If the resist film 63 is thick, the microloading effects become conspicuous and an etching precision, an etching uniformity, an etching throughput and an etched cross section are degraded.
From the above reasons, it is difficult to highly precisely form a gate electrode having a predetermined shape, and the precision of a gate diameter of the gate hole of the gate electrode 62a lowers. In a flat panel display having a number of field emission elements, a variation in gate diameters makes the characteristics of each field emission element different. Namely, the luminance of pixels of the display become irregular.